This invention relates to navigated instrumentation for the preparation of the proximal femur for receiving a prosthetic femoral component. More particularly, the invention relates to a femoral axis finder which can be used with an optical computer-aided navigation system to accurately locate the femoral axis utilizing a shaft with a proximal and distal wedge for insertion in the medullary canal of the femur.
Navigation systems are an interactive operative monitoring system designed to improve the surgical performance and clinical outcome of Total Hip Arthroplasty. A computer-aided, image-less guidance system provides accurate decision making for alignment and orientation of instruments, trials and ultimately implants. The system may provide surgeons pre-operative, intra-operative and post-operative assessments of the patient's joint kinematic measurements. Use of a computer-aided surgical navigation system results in decreased morbidity and shorter hospitalization. Such systems are described in U.S. Pat. Nos. 6,021,343, 6,385,475 and 6,434,415, the teachings of which are incorporated herein by reference.
In the past, the medullary canal of the femur has been opened by standard operative techniques. The surgeon would then digitize the distal and proximal points on a canal axis finder, which finder may be a shaft with a T-handle and a proximal plug for engaging the proximal femur. The shaft is digitized by touching two points on the shaft with a pointer optically coupled to the computer navigation system. Normally, the pointer would have multiple light emitting diodes which, upon activation, emit light which can be read by one or more cameras in the operating room which are connected to the computer-aided navigation system. Digitizing the distal and proximal points on the axis finder allows the navigation system to determine the axis along which a femoral broach has to be aligned to prepare the femoral canal. For patients with varus/valgus deformity, the shaft axis may deviate significantly from the anatomical axis of the femur. This deviation can be calculated by the navigation system and displayed on a CRT showing the proximal femur and the shaft axis.
Specifically, the shaft axis is digitized by inserting the optical tracker tip through the axis finder handle and digitizing a first distal point thereon and then inserting the tracker's tip through the handle to digitize a second point thereon located proximally of the first point on the axis finder. The navigation system checks the distance between the digitized distal and proximal points. Once the shaft axis has been digitized, the surgeon can proceed with preparing the femur. The surgeon removes the axis finder and can then insert a broach into the canal, which broach includes an optical tracker preferably on the broach handle. Thus, the navigation system can align the axis of the broach and the proper anteversion/retroversion angle in the proper frontal offset and varus/valgus angle of the broach. The axes of the broach is shown on the CRT display along with the axis found by the axis finder so that the surgeon can align the axes.
One drawback of this system is that it is difficult to get a snug fit both proximally and distally for all size femurs while using a single shaft axis finder. Thus, the present invention provides for a modular system having a plurality of distal and proximal spacers.